Over the past three years work in the laboratory of Dr. Lubomir Tomaska at Comenius University in the Slovak Republic has been supported by a FIRCA award (TWO 5654) under the parent grant GM31819 to Dr. Jack Griffith at the University of North Carolina. The FIRCA support has resulted in 14 publications and 10 meeting abstracts from the Tomaska laboratory in the past 3 years with two high profile papers just published in TheJournalof Biological Chemistry. These studies have laid the foundation for investigations of telomere structure which are being seen as very significant by investigators both in the US and internationally. The work has been done primarily at Comenius University with 1to 3 month visits each year by Dr. Tomaska and his students to UNC. All funds from the award have gone to his laboratory. In Aim I, the development of the yeast S. cerevisciae minichromosome system will allow the isolation of native minichromosomes for examination by electron microscopy (EM) providing an important new tool that will directly benefit the goals of the parent grant and the objectives of the Griffith laboratory. This minichromosome system will be used by the Tomaska laboratory to continue their examination of the architecture of yeast telomeres. In Aim II, work also initiated under the FIRCA award will continue on the reconstitution of a yeast telosome in vitro using the S. pombe system. In the past funding period the telomere binding protein, Taz1 was shown to form loops at the ends of model S. pombe telomeres. This now places us in a position to understand how Taz1 protein interacts with Pot1 and other telomere binding proteins to form a native telosome. The parent NIH grant has supported the development of methods for examining DNA-protein complexes by EM, and transferring these methods to other laboratories. This technology transfer has now begun with Dr. Tomaska's students learning these EM methods. It is critical that we continue this highly productive international collaboration.